Various embodiments of the present disclosure relate to an alertness device, a seat including the alertness device, and an alertness determination method. In particular, the present disclosure relates to an alertness device having the function of determining alertness, and a seat including the alertness device, and an alertness determination method.
In recent years, a change in a driver's physical condition needs to be detected for stable vehicle operation. Various techniques of detecting and calculating various parameters indicating a driver's state to determine the change in the physical condition, particularly alertness, have been proposed.
For example, Japanese Patent No. 4697185 discloses the following technique. A cardiac cycle sequence is obtained from a heart rate signal, and fast Fourier transformation is performed for the cardiac cycle sequence. The resultant power spectrum is repeatedly integrated to obtain a heart-rate fluctuation low-frequency component power. Driver's alertness is determined based on the heart-rate fluctuation low-frequency component power.
Moreover, Japanese Patent No. 3271448 discloses the following technique. A threshold is first calculated in such a manner that in an awake period, an average of R-R intervals (RRIs) for a predetermined heart rate or a predetermined period of time is obtained, and then a value of integral of an RRI exceeding the average is multiplied by a predetermined factor. Of the RRIs obtained as described above, the RRI(s) exceeding the average is integrated. When such an integrated value exceeds the threshold, it is determined that alertness is lowered.
According to the technique of Japanese Patent No. 4697185, fast Fourier transformation and integration of the power spectrum need to be repeated to calculate the heart-rate fluctuation low-frequency component power as the indicator for determining the presence/absence of drowsiness. Such analysis processing requires time. For this reason, alertness determination is delayed, leading to a delay in notification to a seated passenger. With lack of data continuity, an accurate result cannot be obtained. This leads to a lower robustness such as inexecutable detection due to a missing value and noise contamination and rapid lowering of an accuracy.
According to the technique of Japanese Patent No. 3271448, only the value of integral of the RRI is used as the indicator for determining the alertness. Such alertness determination depends on an RRI within an integral range. For this reason, a detection accuracy is low. In some cases, the sympathetic nerve is instantaneously activated against drowsiness when the drowsiness is initially caused, for example. In this case, the RRI value might be instantaneously lowered in association with activation of the sympathetic nerve. According to the technique of Japanese Patent No. 3271448 using, as a criteria for determination, the value obtained by integration of such an instantaneously-lowered RRI, it is difficult to accurately determine the alertness. For this reason, an alertness device configured such that a load is low in the processing for alertness determination and that the accuracy in alertness determination is high, a seat including the alertness device, and an alertness determination method have been demanded.